(a) Technical Field
The present invention relates to a battery pack case assembly particularly suitable for electric and hybrid vehicles, and a method for manufacturing a battery pack case assembly. More particularly, it relates to a battery pack case assembly for electric and hybrid vehicles formed at least in part from a plastic composite, and a method for manufacturing the same, which provides reduced weight, and improved structural stiffness, collision characteristics, and dimensional stability.
(b) Background Art
In view of rising oil prices and CO2 regulations, studies have recently been focused on the development of eco-friendly vehicles that can replace typical internal combustion vehicles. Quite a few vehicle manufacturers have already succeeded in commercializing and introducing pure electric vehicles and hybrid vehicles into the market.
As shown in FIG. 1, electric vehicles and hybrid vehicles include a battery 1 in the lower portion of the vehicle body or in the trunk space for supplying electric power to an electric motor. The high-voltage battery 1, which is used as a main power source in electric vehicles and hybrid vehicles, has a general structure in which a case assembly houses a plurality of battery packs.
As shown in FIG. 2, a typical battery pack case assembly includes a lower case body 200 for receiving a plurality of battery packs 300, a cover 100 that can be disposed so as to cover and couple to the upper surface of the lower case 200, and various kinds of structure-reinforcing members (e.g. cross member, side member, etc.). The battery pack case assembly may further house additional related parts, such as a Battery Management System (BMS) and a blower, in addition to the battery pack 300.
Since the Distance to Empty (DTE) of electric vehicles is inversely proportional to the vehicle weight, a reduction of weight has become increasingly important in the development of electric vehicles. Thus, attempts to use lightweight materials for various parts of electric vehicles are being actively made.
For example, an attempt to replace typical metallic materials commonly used to form battery pack cases with a plastic composite material is being made. Since the upper cover does not largely support the load of the battery, the upper cover may be manufactured by a typical plastic composite forming method. However, because the lower case and structure-reinforcing members of the case must be capable of sufficiently supporting the load of a battery, these structures have been manufactured by separately press-forming steel parts or inserting a steel reinforced material into a plastic composite.
However, steel materials applied to the lower case and the structure-reinforcing members of the battery pack case assembly need to have a sufficient thickness to ensure stiffness and durability, and parts such as mounting brackets need to be separately mounted. As a result, the total weight of the battery pack case assembly increases.
Under-vehicle body floor mounting structures for a battery pack case assembly are described in EP 1950070, EP 1939028, EP 1939027, EP 1939025, US 2009/0236162, U.S. Pat. No. 7,610,978, and JP 2009-137408. To improve stiffness, these either use a plastic composite in which a steel frame is inserted or adopt a structure in which a separate cross member formed of a steel material is coupled, followed by mounting in a vehicle body cross member and a side member.
However, such battery pack case assemblies formed with steel material increase the weight of the vehicle body, particularly due to the use of numerous steel parts. As such, the total weight increases, which reduces DTE.
Also, large thermoplastic parts, such as the lower case of the battery pack assembly, are prone to shrinkage and/or distortion according to the molding conditions, and post-strains may further be caused by residual stresses due to repeated contraction and expansion from temperature fluctuations during use.
Thus, a method for improving the dimensional stability of parts while reducing the weight using a plastic composite is desperately needed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.